The long-term objective of this project is to elucidate the alterations in hypothalamic function responsible for seasonal breeding in the ewe. Based on preliminary data we hypothesis that anestrus in the ewe results because the long-day photoperiod activates dopaminergic and/or alpha adrenergic neural systems which inhibit the frequency of GnRH release from the hypothalamus. We will first test this hypothesis using classical pharmacological techniques to evaluate the role of these neurotransmitters in suppressing LH-pulse frequency in anestrus and to determine if such inhibitory effects are absent in the breeding season. If the results of these experiments support the hypothesis, we will then examine the functional relationship of these inhibitory dopaminergic and alpha-adrenergic neural systems. Finally, we will begin to determine the anatomical location of these inhibitory neurons using knife cuts, measurement of catecholamine content in specific neural areas and microinjections of antagonists to dopaminergic and alpha-adrenergic receptors into various hypothalamic areas. Techniques include the use of specific agonist and antagonists to dopaminergic and alpha-adrenergic receptors; microdissection of specific neural areas using the Palkovitz punch technique; measurement of catecholamines and their metabolites using high performance liquid chromatography; stereotaxic implantation of cannulae for microinjections and radioimmunoassays of LH, prolactin and progesterone. The results should provide new insights into the physiogical mechanisms producing ovarian inactivity. They may, therefore, lead to new methods for increasing livestock production as well as novel approaches to contraceptives.